vring_desc
size = vq->vq_qsize * sizeof (struct vring_desc);
vq->vq_desc = (struct vring_desc *)base;
phys += vq->vq_qsize * sizeof (struct vring_desc);
_vq_record(struct virtio_softc *vs, int i, struct vring_desc *vd,
struct vring_desc *vdir, *vindir, *vp;
struct vring_desc *vq_desc; /* descriptor array */
size = num * sizeof(struct vring_desc);